Are you asking about Zimbra Desktop (which is where you've posted)? If it's about ZD then the answer is yes, there is on the downloads page. If you're asking about Zimbra Collaboration Server (this thread would be in the wrong forum) then the answer is no, there's no postfix build for Windows (and probably never will be) so there's no ZCS for Windows. This question has been answered before and obviously the Zimbra products that are available and the operating systems they use are listed on the Downloads page.